Self-piercing rivet fastening device with improved die

Abstract

A self-piercing rivet fastening device has a punch that drives legs of the rivet into portions of workpieces that are forced into a die cavity, in order to join the workpieces. Particular surfaces of the die cavity are modified to increase the coefficient of friction in order to prevent tips of the legs of the rivet from breaking through a workpiece adjacent to the die and forming holes.

1. For use in a self-piercing rivet fastening device, a die having walls defining a cavity for receiving portions of components to be fastened when those portions are forced into the die cavity by legs of a self-piercing rivet driven by a punch, wherein predetermined surface portions of the die cavity walls have surface roughness that increases friction between the predetermined surface portions and corresponding portions of a fastened component adjacent to the die that contact the predetermined surface portions, wherein the die cavity walls have a central protrusion with inclined surfaces and the roughness is provided on the inclined surfaces to impede slippage between the inclined surfaces on which the roughness is provided and the corresponding portions of the fastened component. 
     
     
       2. For use in a self-piercing rivet fastening device, a die having walls defining a cavity for receiving portions of components to be fastened when those portions are forced into the die cavity by legs of a self-piercing rivet driven by a punch, wherein predetermined surface portions of the die cavity walls have surface roughness that increases friction between the predetermined surface portions and corresponding portions of a fastened component adjacent to the die that contact the predetermined surface portions, wherein the die cavity walls have a bottom surface and the roughness is provided on the bottom surface to impede slippage between the bottom surface and the corresponding portions of the fastened component. 
     
     
       3. A die according to  claim 1 , wherein the roughness is in the form of streaks extending in a direction to prevent said slippage. 
     
     
       4. A die according to  claim 1 , wherein the roughness is due to lathe or electric discharge processing. 
     
     
       5. For use in a self-piercing rivet fastening device, a die having walls defining a cavity for receiving portions of components to be fastened when those portions are forced into the die cavity by legs of a self-piercing rivet driven by a punch, wherein predetermined surface portions of the die cavity walls disposed to be contacted by corresponding component portions forced into the cavity have surface roughness that provides a coefficient of friction substantially greater than other surface portions of the die cavity walls to impede slippage between the predetermined surface portions and the corresponding component portions. 
     
     
       6. A die according to  claim 5 , wherein the predetermined surface portions of the die cavity walls are inclined surface portions of a die cavity wall protrusion. 
     
     
       7. A die according to  claim 5 , wherein the predetermined surface portions of the die cavity walls are portions of a bottom wall surface of the die.